CA1071932A - Soldering instruments - Google Patents

Abstract

ABSTRACT

Improved soldering-desoldering instruments are described which may be of the temperature controlled type.
The instrument features an improved solder tip consisting of a copper core clad with iron in the form of a cap.
This permits working of the composite structure, for example, by crimping it, by pressing it to obtain a wedge-shaped tip, or by hammering it to elongate it to provide a desired shape. The copper core may be made with a bore to provide an air duct for supplying hot air or for drawing away solder for desoldering operations. The instrument also provides an improved sheath for the heater cartridge and heater to facilitate removal of the solder tip. In addition, the heater element may be provided with one or more sensors, for controlling its temperature and for providing a temperature display.
The temperature display may include a sensitivity control to accommodate the instrument to different solder tips and to convert the instrument to a temperature probe.

Description

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This invention relates generally to soldering or desoldering instruments and particularly relates to soldering tips therefor.
The soldering tip for a soldering instrument must conduct heat from the heater element of the instrument to a component to be soldered in an efficient manner. In addition, the solder tip should readily be wet by the solder ; compound. Furthermore, it needs to be easily cleaned and should not corrode at the usual soldering temperature due 1~ to the influence of flux and other corrosive chemicals.
To this end soldering tips are usually manu:Eactured with a copper core which readily conducts heat. On the t other hand, the copper easily corrodes and does not readily wet solder. There~ore, the copper core has conventionally been plated with a metal such as iron, steel or stainless steel. However, the plating process is fairly complicated and not easily controlled. For that reason9 it has proved to be expensive. In addition, with this process i-t is first necessary to shape the copper core to the desired final form which may include a wedge-shaped tip. Fur-ther, for dif~erent ~' operations solder tips of di~ferent sizes are necessary and this in turn means that a relatively large inventor~ of tips must be kept, each of which must be individually plated.
Furthermore, when a copper core is plated with iron or steel the wall thickness must be uniform and cannot be ~aried. mis may be desirable in certain cases because the wall thickn~ss determines the ease of heat transfer between the copper core and the outer shield: on the other hand, the outer shield provides mechanical rigidity and may have to be thicker at certain areas.
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Another problem encountered in soldering ins-truments is the removal of the solder tip. It may either be necessary to remove a worn out tip and to replace it or alternatively, it may be desired to perform ano-ther soldering operation requiring a different type o~ solder tip.
Frequently, however, and particularly after extended use, the threads of the tip sieze to the stainless steel sheath which conventionally surrounds the heater elemènt.
Therefore, considerable force may have to be used to remove the solder tip which in turn may damage the heater and hence necessitate replacement of the entire front end of the instrument.
For certain applications of temperature-controlled soldering instruments it may bè necessary to operate the I controlling electronics at relatively low voltage and high currentO This may be necessary when thè instrumen-t is operated with dc line voltage. In this case, the silicon-controlled rectifier or power transistor of the instrument may generate considerable heat. Since these components are usually found in the handle of the instrument this may make it di~icult to hold the instrument and may eventually damage the handle.
Therefore, a suitable heat sink is desirable to conduct the heat away from the handle, far example, along the cord of the instrument.
Finally, for the assembl~J o~ complicated components ~ ;~
or for industrial applications it may be desirable to keep a record of the temperatures at which each component has been soldered. There~ore, a temperature sensor would be desirable which permits to display the temperature either by an 1 . . ..
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oscilloscope or a stTip chart recorder.
According to one aspect of the present invention there is provided in a soldering instrument: a substantially cylindrical, thin-walled stainless steel sheath having a reduced diameter front end formed with both internal and external threads which are coaxial with said sheath and ha~ing nut means formed integrally with said sheath; a substantially cylindrical, highly heat conductive heater cartridge coaxially receivable within said sheath and an externally threaded front end threadably engageable with said internal threads of said sheath;
an internally threaded soldering tip threadably engageable over said external threads of said sheath whereby said front end of said heater .
cartridge and the threaded portion of said soldering tip are, when assemblccl, axially coi.nci.dent and in high thermal energy :~low relation-sh:ip w:ith each other; and a hcater element o:E the character to be electrically energized receivable within said cartridge in direct .
thermal contact therewith.
Other features of the present invention such as a temperature sensor permitting temperature display and a construction which facili-tates removal of a solder tip will subsequently be explained.
It should be noted that in the following specification and cla.ims the term "solder instrument" is meant to include both a soldering as wcll as a desoldering device.
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.932 An embodiment of the present invention will now be described9 by way of example, with reference to the accompanying drawings, in which:-Fig. 1 is a plan view of an example of a soldering and desoldering instrument of the present invention;
Fig. 2 is an enlarged plan view of a sheath housing the heater cartridge and heater and to which a solder tip may be connected by threads;
Fig. 3 is an e~ploded view of the sheath and associated parts of Fig. 2 and separately showing the sheath, j the cartridge, the heater and its leads;
Fig. 4 is an exploded view, par-tly in cross-section and illustrating an insertion tool for inserting or remoying the heater cartridge into or from its sheath;
Fig. 5 is an elevational view of a heater wound about I a ceramic core and provided with a thermistor and a i thermocouple as temperature sensors and including a schematic view of a temperature display device;
I Fig. 6 is a slde elevational view of -the cord of a ¦ 20 soldering instrument and a portion of its circuit board illustrating a flexible heat sink consisting o~ a metal braid disposed about the cord and extending to an active heat-generating element;
Fig. 7 is a view in perspective of a portion of the clrcuit board of Figo 6 showing an additional heat sink provided by a copper layer;
Fig. 8 is a view in perspective similar to that of Fig. 7 but showing the cord and i-ts braid applied thereto, the braid extending over a portion o~ the circuit board;
Fig. 9 is a view in perspec-tive similar to that o~
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~L~7~i32 Fig. 8 and illustrating the leads and heat-generating element connected to the circuit board;
Fig. 10 is a perspective view of a copper core and cap or ~acket to be assembled;
Fig. 11 illustrates the assemb:led structure whi.ch is a composite solder tip;
; Fig. 12 is a view in perspective of the structure of Fig. 11 and a crimping device such as a lathe collet;
Fig. 13 is a cross-sectional view of the finished tip after the crimping operation; ~:
Fig. 1~ is a perspective view of another copper core and iron tip o~ different construction;
E'ig. 15 is a view in perspective of the assembled structure having an enlarged cylinder at its rear end;
Fig. '16 is a view in perspective of ~he structure of I Fig. 15 and a collet for crimping the rear portion of the I laminated structure;
Fig. 17 is a cross-sectional view of the structure I after crimping;
Fig~ 18 is a cross-sectional view of the structure of Fig. 17 which has been elongated by hammering which may ¦ be effected by a swedging clevice;
Fig. 19 is a view in perspective of the solder tip shape of Figo 18 provided with a flat wedge as shown -schematically by a press;
Fig, 20 is a pl~n view of the solder tip of Fig. 19 with a stainless steel collar partly in sec-tion;
Fig. 21 illustrates the assembled structure of Fig. 20;
Fig. 22 is a plan view of a structure similar to that of Fig. 21 but without the flat wedges;
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.., Figure 23 is a cross-sectional view of a solder tip in accordance . with the present invention similar to the one shown in Figure 13 but having a steel cap of non-uniform thickness; -Figure 24 is a circuit diagram, partly in block form, to illustrate the use of the soldering instrument of the present invention as a temperature probe and for varying the sensitivity of the temperature readout - in accordance with different types of tips;
Figure 25 is a cross-sectional view of a laminated sleeve or ~;.sheath for the heater element and provided with special rolled threads; :
Figure 26 is a cross-sectional view of a holding collar in accordance with the present invention for holding a -7-. .

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7~3;2 soldering tip to the sheath of the heater element; and ! E Fig. ~ is a cross-sectional view of ~n adap-tor bushing for adapting a threaded element to a holding co~lar of the type illustrated in Fig. ~, the adaptor bushing having rolled threads.
Refer~ing now to the drawings and particularly to Fig. 1, there is illus-trated by way of example a temperature-controlled soldering instrument. This instrument may, for example, be of the type disclosed and claimed in Applicant's prior patent 3,88~,716 of May 13, 1975. The instrument generally includes a solder tip 10, a heater element sleeve or sheath 11 and a handle or housing 12 for a circuit board 14 which supports the active and passive elements of the electronic temperature control circuit of the invention.
I The instrument further includes a cord holding element 15 ¦ which may be flexible or yieldable and through which a cord 16 extends. The cord 16 extends into -the handle 12 as shown at 17.
The circuit board 14 may bear a he~t-generating active element 18 which may, for example, be a power transistor or a silicon~controlled rectifier. A control knob 20 extends through the handle for setting the temperature in the mar~er explained in Applicant's prior patent. The handle 12 may have a flat portion 21 for ease of manufacture. The circuit board 14 is guided by internal groo~es in the handle.
The instrument includes a yieldable a~nular element ~or ring 23 which fits over the end of the handle~ A locking bushing 24 may be provided for locking the heater element sleeve 11 to the handle 12, The sleeve 11 is preferably ~0 provided with an integral nut 25.
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Referring now to Figso 2 ~ 4 there is illustrated the sleeve 11 for the heater element provided wi-th the integral nut 25 at its rear end. The sleeve 11 preferably consists of stainless steel to minimize corrosion and to make it heat resistant. Its front end 26 i~ of reduced diameter and pro~ided with threads 27 which are so arranged that they permit to thread both an ex~ernal and internal member thereto.
As clearly shown in Fig. 4, the sleeve 11 has a ~o substantially uniform inner diameter 28 except for the ~ront portion 26 which has a smaller diameter.
The sleeve 1i is adapted to receive a heater cartridge 30. The external diameter o~ the heater cartridge 30 is such that it will fit into the sleeve 11. Its front end is ~ provided with external -threads ~ of reduced diameter which ! will mate with the internal surface of the threads 27 of the ¦ sleeve 11 when the element cartridge has been introduced.
e heating element 32 ~its the heater cartridge 30 and may consist ~f a coated ceramic material containing the ¦ 20 heater wires. The insulated leads or cords for the heater element 32 are shown at 33.
It should be noted that the rear portion of the heater cartridge 30 is provided at its rear end with an outer conical section 34 which serves the purpose to permit to insert the heater cartridge 30 into the sleeve 110 To this end there may be provided an insertion tool 35 .illustrated in Fig. 4. The insertion tool is hollow as shown and has at its ~ront end 36 an inner conical portion 37 which fits over the outer conical rear portion 34 of the heater cartridge 30.

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Thus as indicated in Fig. 4 by the arrows 38 and ! 40, the heater cartridge 30 is introduced into the sleeve 11 and rotated in a right-hand direction by means of the insertion tool 35. Thus the insertion tool is lightly pressed against the heater cartridge 30 so that the cartridge can be threaded into the internal threads 27 of the sleeve 11. At the same time, the heater element 32 should be inserted into the cartridge 30 with -the cord 33 extending through the hollow portion of the insertion tool.
After the cartridge 30 has been securely threaded the insertion tool 35 may readily be re~oved by an additional rotation which will disconnect -the two elements from each other. In order to remove the heater cartridge 30 -the insertion tool is again inserted into the sleeve 11 and a ¦ tight fit provided which then makes it possible to unthread I the two elements, that is the sleeve 11 from the cartridge 30.
I As shown in dotted lines in Fig. 2, a solder tip 42 may be threaded to the outer thread 27 of the slee~e 11. As explained hereinbefore, the solder tip frequently siezes and 1 20 considerable force may be required to remove it from the i sle~ve 11. To this end there is provided the nut 25 which is made integral with the sleeve 11 and which pre~erably is a hexagonal nut. Hence, the tip may be removed by holding the nut 25 with a suitable hand wrench and by using pliers to unscrew the solder tip 42. In order to facilitate ef~icient removal of the solder tip it should only be screwed ~n finger tight. The sleeve 11 has sufficient mechanical rigidity to resist the torque generated when the tip 42 is removed. ~`
Referring now to Fig. 51 there is illustrated the . ' ' .

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heater element 32 which may be provided with one or two temperature sensors. One sensor is ~or the purpose of controlling the temperature of the heater element. The other temperature sensor serves the purpose to generate a voltage ~hich may be used for displaying the temperature of the heater. It will be understood that a single sensor may be used for both purposes.
The heater element 32 may consist of a ceramic core 45 which may be provided with a plurality of longitudinal ~ 10 holes 46. One of the sensors 47 may serve the purpose to ;~' control the temperature of the heater e:ement in the manner disclosed in Applicant's prior patent. The sensor 47 may, for example, consist of a thermistor. The other sensor ~48 may ser~e the purpose to generate a voltage which may be applied by leads 50 to a temper~ture display de~ice 51.
This may, for example, consist of an oscilloscope ~or exhibiting the temperature of the heater, that is the temperature of the solder tip. On the other hand, if a permanent record is desired a recorder such as a strip chart recorder may be provided.
This will provide an indication on a continuous basis o~ the temperature at which each unit has been soldered.
mis may prove to be o~ importance for control purposes or for checking a large number of units made on an industrial basis~ By way of example~ the leads for the two temperature ~ -sensing devices 47 and 48 may extend through the holes o~
the ceramic core 45. The electric resistance wire is shown at 5~ and may be wrapped around the ceramic core which may subsequentl~ be coated with a suitable material. The circuit board 14 is also shown in Fig. 5 which carries the electric -~ ~ 7 ~ ~ 3 ~

circuit for the tempera-ture con-trol.
As previously referred to, in certain cases the instrument may have to be operated at a low voltage and - high current. This may occur for either ac or dc operationO
In that case, the element 18 becomes a heat-genera-ting element and its heat may have to be rapidly removed from the handle 12 to prevent damage to the handle and to prevent the operator from dropping the instrum~ent when its handle gets too hot to be conveniently grippedO
~A 10 , Such a flexible heat sink has been illustra-ted in - Figs. 6 - 9 to which reference is now made. The instrument is provided again with a cord or cable 16 upon which may be provided a metallic braid 54 consisting of any metal which readily conducts heat such as copper or aluminum. m e braid 54 may be slid over the in3ulation o~ the line cord 16 and may extend over approximately 6" to provide sufficient heat I dissipation.
¦ The cord 16 is electrically connected to the circuit board 14 upon which is mounted the heat generating element 18 which, as explained before, may be a power transistor or a sillcon-controlled rectifier.
As shown particularly in Fig. 7, the circuit board 14 may be provided with a plurali-ty of circuit pads 55 which may consist of copper and to which the input leads 56 of the cord may be connected to supply power to the i~strument.
; Preferably, but not necessarily9 a heat sink 57 is provlded on the circuit board 14 and this heat si~k may -consist of a sheet o~ copper. It is provided between the element 18 and the circuit board 14.
3~ In addition, a portion 58 of the braid 54 is ~ ~ . "

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flattened and extended over the clrcuit board 14 below the position of the element 18. It will, of course, be understood that the forward portion 58 of the baid 54 must be so arranged that it does not make electric contact with the circuit pads 55. As clearly shown in Figure 9, three leads 60 extend from the element 18 into the ci:rcuit board.
Finally, the element 18 may be secured to the circuit board 14 by a nut and screw 61, thereby to provide good thermal contact between the element 18, the forward braid portion 58 and the copper heat sink 57.
It will be evident now that a flexible heat sink has been provided which will rapidly dissipate heat generated by the element 18. lhere will, of course, be a certain temperature gradient bctween the element 18 and the outer end of the braid 5~ on the cord 16. It will also be evident that the cord 16 has to be insulated in the usual manner. ~ -Because the braid, as well as the cord, are flexible the heat sink in essence is flexible and will not impede the mobility of the instrument.
Referring now generally to Figures 10-22, there are illustrated various solder tips. These solder tips are characterised by having a copper core and a cap consisting of steel or iron, that is preferably of so-called Armco R iron.
This material is conventionally used for transformer cores.
It is characterised by its resistance to corrosion, for example to solder flux, at elevated te~peratures. It also is readily wetted by solder and is easy to clean.
Thus referring specifically to Figures 10-13 there is illustrated in a number of steps the manufacture of a . lE;
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~6~7~9~32 large spade solder tip. The solder tip comprises a copper core 63 which has a conical forward end 64, Qn intermediate cylindrical portion 65, a portion 66 forming a reverse cone forming a small angle with a central axis and a hollo~ rear portion 67 of enlarged diameter provided with internal threads 68 for attachment to the heater sleeve 11.
Also shown in Fig. 10 is a thin-walled cap or jacket 70 pre~erably made of Armco~steel. It has a shape to fit the copper core 63 and hence is provided with a ~orward ; conical portion 71 and a rearward cylindrical portion 720 Its interior i~ hollow as shown at 73 to accept the conioal portion 64 and also has a hollow cylindrical rear portion 74 to fit over the cylinder 65 and cone 66 o.~ the core 6~.
The core 63 and cap 70 are now assembled as shown in Fig. 11 with the cap providing a tight fit with the core.
Thus a laminated or composite structure 75 is formed which has a front end entirely surrounded by the cap 70. The laminated structure 75 consisting of core 63 and cap 70 is now connected, fcr example, by crimping it by a suitable crimping device 76 which may take -the form of the collet of a lathe. Hence when the collet is tightened, the cylindrical rear portion 72 o~ the cap 70 is pressed against the rear portion of the copper core 63, whereby the rear portion o~
conical shape 66 becomes cylindrical due to the flow of the copper. me finished structure is shown in Fig. 13 and has a uni~ormly cylindrical rear portion 77 with a steel cap 78 and a copper core 80. The rear portion 67 remains unchanged and has internal threads 68.
Thus, the reverse bias portion 66 of the copper core simply facilitates the connecting or crimping and permits a ~ 32 portion of the copper to flow toward the rear.
The unclad portion 67 of the copper may be plated with a suitable metal. For example~ -the plating may be done with nickel or with hard chromium or with both. If the rear portion is only plated with chromium the plating may be done before the shaping or working of the solder tip~ If it is ; only plated with nickel it preferably is done after the working of the solder tip.
Another embodiment of the present invention is - 10 illustrated in Figs. 14 - 21 to which reference is now made.
This will provi~e a so-called small spade solder tip or dip tip. As shown in Fig. 14, there is again provided a copper core 8Z and a steel or Armco iron cap 83. The copper core 82 may have an elongated f`orward conical portionJ a cylindrical intermediate portion 84, a rear conical portion ;l 85 as previously disclosed, and an internally threaded cylindrical rear portion 86. The cap 83 has an internal shape 87 to accept the copper core and again has a conical forward opening and a rearward cylindrical opening 88.
llhe two portions are now assembled in the manner previously described as shown in Fig. 15 to provide a c~mposite or laminated structure 90. The structure 90 may again be crimped by the collet C as shown in Fig~ 16 or otherwise connected and the resulting product is shown in Fig. 17. The structure has an elongated conical forward ~ection 91, a cylindrical intermediate section 92 and the ~ -original rear section 86 with internal threads 93.
As illustrated in Fig. 18, the composite structure 90 is now shaped to provide the structure 95. This may be effected by hammering or peening by hand or by the swedging . .

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machine 96. This consists of two portions 97 and 98 between which the structure 95 is inserted. The entire structure is then rapidly hammered while being rotated about the solder tip as shown by the arrow 100.
As a result the structure 95 hias a forward conical - portion 101 and an intermediate concav~e portion 102 with a cylindrical intermediate portion 103. ~;
As shown in Fig. 19, the structure95 may additionally be provided with a wedge shape ~hown at 105 and this may be effected by the press 106 which will flatten out two sides of the forward portion 101 of the solder tip.
The finished structure 95 may now be provided with a stainless steel sleeve 108 having internal threads 110 at its rear portion and an internal diameter to fit over the rear portion 86 of the solder tip 95. It is provided with a shoulder 111 to be retained by the rearward cylinder 86 so that the locking sleeve 108 may be screwed onto th~
; heater sleeve 11.
¦ Preferably, the locklng sleeve 108 is made of 1 20 stainless steel and it may be coated wi-th an anti-seize ! compound. Such a locking sleeve has the advantage that the soldering tip need not be directly removed from the heater sleeve 11, but only the locking sleeve 108 needs to be unscrewed. Since the sleeve 108 consists of stainless steel it is mechanically strong and can be made resistant to seizing.
The finished structure 95 with the attached locking slee~e 108 is illustrated in Fig. 21.
As shown in Fig. 22, the step of providing a wedge ~0 shape 105 as shown in Fig. 19, may be omitted. Otherwise 7'l~3;~:

the structure of Figure 22 is identical to that of Figure 21.
It may be advantageous for certain purposes to provide a cap for the copper solder core having a variable thickness. Where the cap is relatively thin, the heat transfer from or to the copper core is facilitated.
On the other hand, where the thickness of the cap is larger the resulting laminated or composite structure is mechanically stronger. Such a tip 155 is illustrated in Figure 23. This tip is generally similar to that shown in Figure 13 and again has a copper core 80 as previously desc-ribed. However, the steel cap or jacket 156 has a thin forward portion 157 and a relatively 10 thicker rearward portion 158 which may form a cylindrical opening 160.
As a result the heat transfer to the tip portion 157 of the solder -tip is facilitated; at the same time the rearward portion 158 if made mechanically stronger.
~ s indicated in dotted lines in l7igure 17, the steel jacket 16:l again may have a thicker or stronger rear portion 162 for the same purpose.
A similar construction is shown in Figure 18 where again the rearward portion 103 of the steel cap may be made thicker as shown at 164.
;! It will be understood that the construction shown in dotted lines and in Figure 22 and previously discussed is optional and that it may be sufficient for many purposes to provide a cap of uniform thickness.
In some cases, it may be desirable to use the temperature controlled instrument of the type illustrated in Figure 1 as a temperature probe, that is for simply measuring the temperature of a solder connection or similar hot objects. In addition, it may be desired to vary the sensitivity of the temperature display. How thls can b~ effected is lllustrated in Figure 24.
There is illustrated a digital temperature meter shown in box 170 for providing a digital temperature readout. The power may be connected by a plug 171 having two power leads 172 and a ground connection 1~9. The power may be turned on and off by the switch 173 which interrupts one of the power 30 leads 172. An electronic module 174 is provided which will convert the ~ . .

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~L~7~32 voltage received from a temperature sensor into a digital readout as shown at 175. i The digital temperature meter is connected by another plug 176 to a temperature controlled instrument of the type illustrated in Figures 1 and 5.
Thus, the plug 176 connects to the circuit board 14 as shown in Figures 1 and 5. The heater element illustrated schematically at 32 may again be provided with a thermistor 47 for controlling the temperature of the instrument and a thermocouple 48 for measuring the temperature at the tip.

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; The thermocouple 48 has a pair o~ leads 177 which connect through the plug 176 into -the electronics module 174 through a switch 178 having a switch arm which may be connected to a set of graduated resistors 180 each having a different resistance or ~irectly through lead 181.
Hence by rotating the swi-tch arm of switch 178 more or less resistance may be connected in-to the circuit consisting of the leads 177 and the thermocouple 48. In this manner the sensitivity of the electronics module 174 may be varied depending on the type of solder tip that is being used.
There may also be provided anot~er switch 182 ganged to the switch 178 as shown which connects the input power leads 172 to a watt/hour meter 183 and through the plug 176 to the circuit board 14.
When it is desired to utilize the instrument as a temperature probe the solder tip is removed and both switches 178 and 182 are rotated clockwise so that ~he switch arm o~
j switch 178 connects to lead 181 while the switch arm of switch 182 connects to contact 179, thereby to disconnect the watt/
hour meter~ This will also disconnect the power to the circuit board 14.
There may also be provided an output buffer 184 connected to the input of the electronics module 174~ thereby to obtain a digital temperature readout from the auxiliary thermocouple.
In connection with Figs. 2 - 4 there was disclosed and illustrated an embodiment of the invention which facilitates removal of the solder tip from the sleeve or sheath o~ the heater element. Another construction which will also facilitate removal of the solder tip and prevent damage . _~ _ 1~ ~ .
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~ 2 6 E to the heater element is illustrated i~ Figs. ~ 4 to ' which re~erence is now made. Thus Fig. 33 illustrates at ; 190 a modified composite sheath or sleeve for the heater elementO It consists of an outer cylindrical sleeve 191 which preferably consists of stainless s-teel and an inner copper cylinder 192 9 the two forming a composite or laminated structure. The forward end o~ the sleeve 190 is closed by a copper core portion 193 having a conical inner opening 194.
Preferably, the two elements 191 and 192 are so made that they provide a ~lose fit.
Both elements are now -threaded together as shown at 195. The threads 195 are specially designed to have a ro~lded i shape as shown at 196. This permits to keep the inner diameter ~97 as large as possible to improve the heat flow ~orward to ~ the soldering t~p. On the other hand, the stainless steel is ; su~stan~ially corrosion proo~ and permits easy removal of the soldering tip even after long usage. The threads 195 ; are preferably rolled. The high point 196 o~ the 'chreads is c thicker to add maximum strength to the thread. The radiuses of the high portions 196 and the low portions 197 are such that they do not substantially stress the stainless steel sleeve of the laminate. It will be understood that a solder tip such as shown at 42 in Fig. 2 may be threaded onto the threads 195.
Instead of threading the solder tip directly to the structure of Fig. ~ it is feasible to utilize a holding collar such as previously discussed in connection with, for example, Fig. 20. Such a holding collar 200 is illustrated , in Fig. ~4. It is provided with in-ternal rolled threads 201.
~0 The holding collar is made to release easily from a stainles~
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, steel slee~e of the type illustrated in Figures 2-4. The lower portion or radius 202 of the threads is weaker than the higher portion 203 and hence would tend to strip first.
It will be realized that ordinarily stripping of the threads will not occur. If the holding collar 200 is made of stainless steel, seizure is very unlikely. The soldering tip 204 is provided with an enlarged cylindrical portion 205 at its rear end which is retained by the shoulder 206 of the holding collar 200.
In some cases it may be desirable to provide an adaptor for the normal thread of the stainless steel sleeve or sheath 11 as shown in Figures 2-4. Such an adaptor is shown in ~igwre 27. The original portion Oe the sleeve is shown at 1l~ haYing threacls 27'. The adaptor bushing 208 threads over the threads 27' and is provided on its outside with the roller threads 210 as discussed in connection w~ith Figures 25 and 26. A portion of a holding collar 211 is also shown in Figure 27 and this holding collar may be identical with the holding collar 200 of Figure 26. It is shown with threads 212 which are relatively pointed and thin so that they will easily strip from the holding collar. This adaptor will facilitate converting a tool having ordinary threads to the rolled threads illustrated in Figures 25 and 26.
The constructions shown in Figures 25-27 have the following advantages. The outer sheath provides greater mechanical strength and the threads have a long life. The ;-~
heat path from the heater element to the soldering tip ls relatively large to provide for rapid transfer of heat. The -~
construction will solve the tip seizure problem and perrnit the use of thin, high-heat soldering elements. The threacls ' ~.

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are characterized by high resistance to corrosion and by minimum sei.zure of the threads. The radius of the threads has a low profile. The rolled threads shown can be econcmically manufactured in mass production~ Finally, during the installation and removal of the tip the heater element suffers substantially no stress.
; There has thus been disclosed an improved soldering instrument. me new soldering instrument features an improved sleeve for the heater element which facilitates removal of the soldering tip even after long use. This is accomplished by the provision of a special nut made integral with the sleeve so that the tip can be readily removed without damaging the heater element. Furthermore, the heater may be provlded with one or more sen.sors which permit a display of the temperature. The sensitivity of the heater may be varied in accordance with the type of tip utilized and various readouts may be provided. A new process has been disclosed ~ for manufacturing laminated solder tips and for shaping them ¦ into any desired shape, for example, by h~mering or peening the laminated structure. The thin-walled steel cap of -the structure may either be made o~ uniform thickness or non-. . . . . .
uniform thickness to facilitate heat transfer at the forward end and to provide greater mechanical strength at the rearward end. Another construction of the heater element sleeve , features rolled threads to also facilitate removal of the solder tip and better heat transfer thereto.
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Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a soldering instrument: a substantially cylindrical, thin-walled stainless steel sheath having a reduced diameter front end formed with both internal and external threads which are coaxial with said sheath and having nut means formed integrally with said sheath; a substantially cylindrical, highly heat conductive heater cartridge coaxially receivable within said sheath and an externally threaded front end threadably engageable with said internal threads of said sheath; an internally threaded soldering tip threadably engageable over said external threads of said sheath whereby said front end of said heater cartridge and the threaded portion of said soldering tip are, when assembled, axially coincident and in high thermal energy flow relationship with each other; and a heater element of the character to be electrically energized receivable within said cartridge in direct thermal contact therewith.

2. The invention according to claim 1 in which said cartridge is axially shorter than said sheath and which is provided with insertion tool engaging means disposed contiguously to its rear portion for providing threading torque thereto.

3. The invention according to claim 2 in which said insertion tool engaging means comprises a rearwardly converging conical surface for frictionally engaging an external insertion tool.

4. A temperature controlled soldering instrument as claimed in claim 1; a first sensor disposed at the front end of said heater and in the neighborhood of the solder tip of the instrument; means including said first sensor for controlling the temperature of said heater element and for displaying the temperature of said heater element.

5. An instrument as claimed in claim 4, wherein a second sensor is provided in the neighborhood of said first sensor and a temperature display device connected to said second sensor for continuously displaying the temperature of said heater element.

6. An instrument as claimed in claim 5, wherein said first sensor consists of a thermistor and said second sensor consists of a thermocouple.

7. An instrument as claimed in claim 5, wherein said second sensor is adapted to be coupled to a digital temperature meter.

8. An instrument as claimed in claim 7, wherein a resistive network is interposed between said second sensor and said digital temperature meter for varying at will the sensitivity of said meter in accordance with differ-ent types of solder tips.